1. The field of art to which the invention pertains includes the art of fluid handling and line condition change responsive valves therefor.
2. Customary practice in many fluid handling and dispensing systems includes installation of an automatic shutoff valve of sorts for preventing inadvertent flow other than when expressly intended or authorized. Such valves are particularly useful, if not required by many local codes, where dispensing combustible commodities such as gasoline. A pilot actuated shutoff valve commonly used at gasoline service stations between the pump and hose of each dispenser is disclosed in U.S. Pat. No. 3,538,944.
At a typical gasoline service station, more than one dispenser is provided for delivering each available grade of gasoline with each such dispenser being frequently connected in parallel with others receiving their gasoline in a common distribution system from an underground storage tank. Actuating any one or more of the dispensers energizes the pump which in turn pressurizes the entire distribution system thereby increasing the inlet pressure at all of the dispensers whether actuated or not.
It is essential under those conditions that the installed shutoff valve be effective to prevent flow, even in leakage quantities, through those of the dispensers which are not activated. At the same time, the inactive dispensers continue to contain gasoline at the system shutdown pressure which is subject to increase by exposed temperature increases or the like. This has necessitated use of a separate check and pressure relief valve in order to prevent breakdown of the equipment.
Despite the problems and expense associated with the separate valves in the manner of the prior art, it has not heretofore been known how to combine the functions of on-off, check and relief embodied in a single valve construction.